1. Field of the Invention
This invention relates to a magnetic head assembly in a device for driving a double-sided magnetic recording medium in the form of a disk, i.e., of the type in which information can be recorded on, and reproduced from, both sides thereof.
2. Description of the Prior Art
There is known a device for driving a magnetic recording medium in the form of a disk which can have information recorded on, and reproduced from, both sides thereof. Three types of devices are known and differ from one another in the position of a magnetic head which is supported on a gimbal spring. The first type of device is of the type having a movable top and a fixed bottom and has a gimbal spring provided on a holding case. The second type is of the type having a fixed top and a movable bottom and has a gimbal spring provided on a carriage. The third type is of the type having a movable top and a movable bottom and has a gimbal spring provided on both of a holding case and a carriage. The first type is widely used, as it has a reference plane which is easy to define, since the carriage is directly guided by a guide bar. The second type has a reference plane which is difficult to define, since the holding case is rotatably supported on the carriage. The third type has a reference plane which is still more difficult to define, though it is satisfactory in followup characteristics. Therefore, it is usual to limit the movement of the gimbal spring on the carriage. Thus, it is, in fact, of the type having a movable top and a semi-stationary bottom.
A further improvement is expected from the second type of device, since it can be superior to the first type in followup characteristics, though it has a reference plane which is more difficult to define. The first type of device has two movable portions on the holding case, i.e., the gimbal spring and the junction between the holding case and the carriage. A secondary delay occurs to those two portions when they follow the deformation of a magnetic disk. On the other hand, the second type of device has no such delay, as only the gimbal spring on the lower magnetic head is movable, while the position of the upper magnetic head does not appreciably change. A device of the second type is typically shown in FIG. 3.
The magnetic head supporting mechanism shown in FIG. 3 consists mainly of an arm (holding case) 34 carrying a magnetic head 32 and a carriage 36 on which a magnetic head 33 is mounted. The arm 34 is rotatably supported on a leaf spring hinge 35 projecting from the sidewall 36a of the carriage 36. A coiled spring 37 is provided between the arm 34 and the top wall 36b of the carriage 36 for applying an appropriate load to the arm 34. The upper magnetic head 32 is secured to the bottom of the arm 34. The lower magnetic head 33 is supported by a gimbal spring 38 on the bottom wall 36c of the carriage 36. The upper and lower magnetic heads 32 and 33 face each other and a flexible magnetic disk 31 can be held therebetween. The bottom wall 36c of the carriage 36 has a through hole formed below the gimbal spring 38. A leaf spring 41 has one end secured to the bottom wall 36c and extends into the hole. The leaf spring 41 has a free end provided with a pivot 40 engaging the bottom of the gimbal spring 38 and thereby supporting it resiliently thereon.
When the disk 31 is disposed between the magnetic heads 32 and 33, the leaf spring 41 allows the lower megnetic head 33 to move down and a balance is reached between the downward force of the coiled spring 37 and the upward force of the leaf spring 41 to hold the disk 31 in a stable position in which the disk 31 has a reference plane extending in parallel to the mutually facing surfaces of the magnetic heads 32 and 33 so that the disk 31 may be driven for recording or reproduction purposes.
The device as hereinabove described has, however, a number of drawbacks. Only that corner 32a of the upper magnetic head 32 which is closer to the hinge 35 contacts the disk 31 before the lower magnetic head 33 is moved down, and the force of the coiled spring 37 is concentrated on the corner 32a. The corner 32a is, therefore, very likely to damage the disk 31. When the lower magnetic head 33 is moved down, the gimbal spring 38 is greatly deformed and if random vibration is transmitted from the disk 31 to the magnetic head 33, the gimbal spring 38 is likely to resonate and produce an audible resonant sound. This phenomenon may be called the sobbing of the head.